Formation of icosahedral clusters and spin freezing in RE(Fe_1-xAl_x)₁₃ amorphous alloys

The formation of icosahedral clusters in RE(Fe_1-xAl_x)₁₃ (RE: La, Y, Ce and Lu) amorphous alloys have systematically been investigated. The spin-glass behavior and the magnetic phase diagrams are closely related with the interatomic distance of Fe-Fe pair in the icosahedral clusters formed in the amorphous phases. The existence of icosahedral clusters in the RE(Fe_1-xAl_x)₁₃ amorphous alloys was confirmed by X-ray diffraction, although the formation in the crystalline state restricts to only RE = La. Mössbauer spectra were also found to be consistent with the X-ray diffraction data. The nearest interatomic distance, 0.255 nm, of Fe-Fe pair in the icosahedral clusters is unchanged in the RE(Fe_1-xAl_x)₁₃ amorphous alloys and hardly depends on the kind of RE elements. Such a short distance brings about a re-entrant spin-glass state due to the appearance of antiferromagnetic interactions, and the spin freezing temperature is scarcely affected by the variety of RE elements. On the other hand, the Curie temperature depends on the atomic size of REs.